A blow molding method, a gas injection molding method and the like are well-known as a process for producing a hollow molded article using a thermoplastic resin.
However, in the skin material-lamination molding by a blow molding method, it is impossible to control the wall thickness of a skin material-laminated hollow molded article of thermoplastic resin, and hence, there is such a problem that it is difficult to obtain a molded article having a uniform and desired wall thickness. In addition, there are such many problems that the thermoplastic resins used are limited by their flow characteristics, viscosity and the like in the molten state and the shape of the molded article cannot respond to a shape having a high blow ratio.
On the other hand, a gas injection molding method is known as a process for molding a thermoplastic resin hollow molded article which is hardly affected by the flow characteristics, viscosity and the like of the molten thermoplastic resin, capable of controlling the wall thickness and can respond to a shape having a high blow ratio; however, according to said method, it was difficult to produce a skin material-laminated molded article in which the skin material is an exterior decorative surface though said method was applicable to a process for producing a molded article consisting of only a resin without using a skin material.